Synthesis of Poly(propylene oxide)–Poly(N,N′-dimethylacrylamide) Diblock Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Solution

Sterically-stabilized diblock copolymer nanoparticles comprising poly(propylene oxide) (PPO) cores are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous solution. N,N′-Dimethylacrylamide (DMAC) acts as a cosolvent for the weakly hydrophobic trithiocarbonate-capped PPO precursor. Reversible addition–fragmentation chain transfer (RAFT) polymerization of DMAC is initially conducted at 80% w/w solids with deoxygenated water. At 30–60% DMAC conversion, the reaction mixture is diluted to 5–25% w/w solids. The PPO chains become less solvated as the DMAC monomer is consumed, which drives in situ self-assembly to form aqueous dispersions of PPO-core nanoparticles of 120–190 nm diameter at 20 °C. Such RAFT polymerizations are well-controlled (Mw/Mn ≤ 1.31), and more than 99% DMAC conversion is achieved. The resulting nanoparticles exhibit thermoresponsive character: dynamic light scattering and transmission electron microscopy studies indicate the formation of more compact spherical nanoparticles of approximately 33 nm diameter on heating to 70 °C. Furthermore, 15–25% w/w aqueous dispersions of such nanoparticles formed micellar gels that undergo thermoreversible (de)gelation on cooling to 5 °C.


Table of Reagent Quantities and Intermediate Conversions
Table S1.Summary of reagent quantities used for DMAC polymerization using either a PPO 40 -TTC or a PPO 60 -TTC precursor.Initially, this polymerization was conducted at high solid concentration, with subsequent dilution via addition of deoxygenated deionized water.
Instantaneous DMAC conversions at the time of addition of water were determined via 1 H NMR spectroscopy.

S3
Supplementary data for the characterization of PPO-TTC percursors

Figure S1 .
Figure S1.Assigned 1 H NMR spectrum (CD 2 Cl 2 ) obtained for the PPO 40 -OH precursor.Comparison of the aromatic benzyl proton signals a-c at 7.37 ppm with that of the PPO proton signals g, f and e at 1.16 ppm, 3.43 ppm and 3.55 ppm enabled determination of a mean degree of polymerization of 39.6 ± 0.6 via end-group analysis.

Figure S2 .
Figure S2.Assigned 1 H NMR spectrum (CD 2 Cl 2 ) obtained for the PPO 60 -OH precursor.Comparison of the aromatic benzyl proton signals a-c at 7.37 ppm with that of the PPO proton signals g, f and e at 1.16 ppm, 3.43 ppm and 3.55 ppm enabled determination of a mean degree of polymerization of 60.4 ± 0.6 via end-group analysis.

Figure S4 .Figure S5 .
Figure S4.Assigned 1 H NMR spectrum (CD 2 Cl 2 ) of the functionalized PPO 40 -TTC precursor.Comparison of the integrated proton signal j at 1.91 ppm assigned to the methyl group of the RAFT agent with that of the unique PPO proton signals e and g at 1.16 ppm and 3.55 enabled determination of a mean degree of esterification of 97 ± 1 %.

Figure S6 .
Figure S6.DMF GPC curves (UV detector set at λ = 305 nm) recorded for the CEPA RAFT agent (black curve) and the PPO 60 -TTC (blue curve) and PPO 40 -TTC (red curve) precursors.GPC analysis of CEPA required addition of glacial acetic acid (but not LiBr) to the DMF eluent: this prevented ionization of the carboxylic acid group of this RAFT agent.

Figure S9 .
Figure S9.DMF GPC curves recorded using (a) a refractive index detector and (b) a UV detector set at λ = 305 nm for a PPO 60 -PDMAC 120 diblock copolymer prepared by reverse sequence aqueous PISA initially at 80 or 90% w/w solids content at 60 o C and a PPO 60 -TTC precursor.Conditions: [PPO n -TTC]/[AIBA] molar ratio = 5.0.[N.B.Diblock copolymer GPC curves are only shown up to an elution time of 17.9 min to omit the signal attributed to LiBr (see FigureS3).GPC analysis of the PPO precursor was performed in the absence of any LiBr salt].

Figure S11 .Figure S12 .
Figure S11.(a) Intensity-average and (b) number-average particle size distributions obtained by DLS analysis of a 1% w/w aqueous dispersion of PPO 60 -PDMAC 120 nanoparticles at 20 o C (blue data) and 70 o C (red data).

Figure S13 .
Figure S13.DLS analysis of PPO 60 -PDMAC 120 nanoparticles prior to (red data) and after freeze-drying and redispersal in deionized water at 1% w/w solids (blue data).